The efferent connections of the feline nucleus cuneatus

Abstract

Nucleus cuneatus projections to nucleus ventralis posterolarteralis pars medialis (VPLm) and other thalamic as well as midbrain and medullary nuclei were studied in cats using the Fink-Heimer I silver technique. Single electrolytic lesions of very small size were made stereotaxically in different zones of nucleus cuneatus under electrophysiological control. All zones studied projected to contralateral VPLm in a pattern of discrete terminal arborizations or clusters, which were organized in onionskin-like dorso-ventral laminae. The clusters of degeneration varied in size and density according to their dorsoventral location within VPLm. Those in dorsal areas were smaller in diameter (50-125 mu) and contained less dense amounts of degeneration than clusters (150-300 mu) in more ventral regions. The clustered terminal arborizations mirrored the organization of the VPLm neuronal clusters, themselves. Terminations within VPLm were topographically organized, but were completely inverted, i.e. dorsal nucleus cuneatus projected to ventral VPLm and ventral to dorsal, lateral to medial, and medial to lateral VPLm. A ventral zone of nucleus cuneatus, which contained "deep" units, projected to a separate dorsal zone of VPLm. In addition to its classical connection with VPLm, nucleus cuneatus projected to the following contralateral brainstem or thalamic nuclei: medial and dorsal accessory olives, external nucleus of the inferior colliculus, ventrolateral part of the superior colliculus, nucleus ruber, medial geniculate nucleus pars magnocellularis, suprageniculatus, medial and lateral divisions of the posterior thalamic nuclear group, zona incerta, and Fields of Forel. Very sparse amounts of degeneration were also present within nuclei ventralis posteromedialis (caudal pole) and ventralis posterolateralis pars lateralis. The brain-stem and thalamic projections of the dorsocaudal part (cell nest region) of the cuneate nucleus were more restricted than those of its rostral and ventral regions. The clusters of both the VPLm neurons and cuneate terminations within VPLm provides an anatomical basis for the functional characteristics of synaptic security, fine grain somatotopia and modality specificity so prominent in the dorsal column nuclei-medial lemniscal system.

Synaptic inputs of feline rubrospinal neurons from the parietal association cortex, pretectum and medial lemniscus, and their lesion-induced sprouting.

“…Furthermore, in agreement with previous physiological studies (MASSION, 1961;NISHIOKA and NAKAHAMA, 1973;ECCLES et al, 1975b), there are peripheral inputs to RN which are not mediated by the cerebellum or cerebral cortex. Our result has shown that ML is the monosynaptic input to RN thus corroborating previous histological and physiological studies (CAJAL, 1909(CAJAL, -1911HAZLETT et al, 1972;HAND and LIU, 1966;PADEL and JENESKOG, 1981;Padel, personal communication;Fanardyan, personal communication).…”

Somatosensory nucleus in the torus semicircularis of cyprinid teleosts

“…Overall, the afferent connectional pattern to the teleost TSe is quite similar to that of the intercollicular nucleus in amniotes, as suggested by Muñoz et al (1997). An alternative interpretation, however, is that the teleost TSe corresponds to the same-named toral nucleus in mammals receiving fibers from the spinal trigeminal nucleus, nucleus X, dorsal column nuclei, and spinal cord (Hand and Winkle, 1977;Aitkin et al, 1981;Coleman and Clerici, 1987;Li and Mizuno, 1997) and to the somatosensory receptive toral zone in other vertebrates (birds: Wild, 1989;amphibians: Muñoz et al, 1997).…”

Organization of Projections from the Gracile, Medial Cuneate and Lateral Cuneate Nuclei in the North American Opossum

“…A compa rable finding has been reported for the cat [Cheeket al, 1975] and rat [Lund and Web ster, 1967]. Rather, most of those cells ap pear to innervate extrathalamic regions such as the cerebellum (the opossum, pres ent investigation; the cat, Rinvik and Walberg, 1975;Cheek et al, 1975), the inferior olive (the cat, Berkley, 1975;Berkley and Hand, 1976;Hand and Van Winkle, 1977;Boesten and Voogd, 1975;Groenwegen et al, 1975], the spinal cord (the opossum, Crutcher et al, 1978, and present study; the cat, rat and monkey, Burton and Loewy, 1977), as well as various brain stem nuclei (the cat, Lund and Webster, 1967;Hand and Van Winkle, 1977).…”